PENNSYLVANIAN-PERMIAN

• Quiescence

• Volcanism Ceases

• Havallah Basin of Extension?

• Passive Margin (?) Shelf Sedimentation

Ancestral Rockies Uplift

• Paradox Basin & Uncompaghre Uplift

• Transgressive Association

• Allegheny Events in Marathon/Ouachita Belt

1 Sonoma Orogeny

•Late Permian and early Triassic age

•Change from passive to active margin conditions

•Emplacement of Golconda Allochthon

•Truncation of NE-SW trending continental margin in Mojave area

•Formation of a new active margin

2 Golconda Allochthon

• Upper plate

– Argillite, sandstone, volcanic rocks

• Lower plate

– Carbonates and clastics

Havallah Basin

• Source for Golconda rocks

• Either a passive margin or a marginal basin

• Source of materials

– Sediments from Antler thrust to the east

– Andesitic source to the west

Stratigraphy of Havallah Basin

• Early Mississippian Sediments from Antler Thrust Belt • Upper Mississippian Pillow Lava and Radiolarian Chert • Penn/perm Carbonate Turbidities from the East • Early Permian Basaltic Volcanism • Late Permian Arc Derived Detritus

3 Related Depositional Consequences Environments • Continental shelf to the east • Havallah Basin Closed – Penn/Perm transgressive marine • Volcanic Basinal Rocks Thrust sequences Eastward • Island arc to the west • West Facing or East Facing Arc? – Andesite through rhyolites preserved in Klamath Mts. and Sierra Nevada

Nevadan Orogeny (162-144 Ma) • General – Turbidite Deposition Across Ophiolites and Synchronous Deformation Define Orogeny • Plate Edge – Fore Arc Basins Source of Ophiolites • Isolated Magmatism as Small Plutons

Plate Interior

• Foreland fold and thrust belt • Major sediment source to the west • Trough near the highland • Syntectonic intrusions – Orogenic highlands Nevada, Utah, Idaho

4 Plate Kinematic Patterns

• NW acceleration to 200 Km/Ma

• Sinestral tangential motion

– Relative to plate edge

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